Craig,
I think the picture posted back then was of a 36" gauge wood passenger coach in the Guatemala City yards. There are several steel coaches throughout, and a few wooden coaches scattered. Everything in Guatemala, currently, is 36" gauge. Rail Development Corp. mentioned that they would like to develop the Pacific side into standard gauge. East of Esquintla, standard gauge would not be practical.
The diversity of the rail-equipment there would drive the narrow gauge model railroaders crazy - like finding hidden treasures. Much of the equipment in Guatemala was made in Guatemala.
Since you said yellow, attached is a picture of a yellow steel coach that was part of our east-bound steam conist.